How to set HTTP status code in response in Go (Golang)

Table of Contents

Overview

WriteHeader method of the ResponseWriter interface in net/http package can be used to return the status code from a golang server.

In GO a response is represented by the ResponseWriter Interface. Here is the link to the interface –

https://golang.org/pkg/net/http/#ResponseWriter

ResponseWriter interface is used by an HTTP handler to construct an HTTP response. It provides three functions to set the response parameters

Header – For writing response header

Write([]byte) – For writing response body

WriteHeader(statusCode int) – For writing the http status code

As you can see WriteHeader function takes statusCode as input and that status code is sent in the HTTP response. While Write function can be used to set the response body. It is to be noted that if WriteHeader is not called explicitly then the call to Write function will call the WriteHeader function internally with status code 200 which is StatusOk.

Example

Let’s see an example of sending http status code and body

Below is the program for the same

package main

import (
	"encoding/json"
	"log"
	"net/http"
)

func main() {
	handler := http.HandlerFunc(handleRequest)
	http.Handle("/example", handler)
	http.ListenAndServe(":8080", nil)
}

func handleRequest(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusCreated)
	w.Header().Set("Content-Type", "application/json")
	resp := make(map[string]string)
	resp["message"] = "Status Created"
	jsonResp, err := json.Marshal(resp)
	if err != nil {
		log.Fatalf("Error happened in JSON marshal. Err: %s", err)
	}
	w.Write(jsonResp)
	return
}

Here we are using the WriteHeader function to specify the 201 http status code. Similarly, we can send pass any of the status codes listed here to the WriteHeader function

https://golang.org/src/net/http/status.go

Also it uses the Write function to return the response body. The above code returns the below JSON request body back in response

{"message":"Status Created"}

Run the above program. It will start a server on 8080 port on your local machine. Now make the below curl call to the server

curl -v -X POST http://localhost:8080/example

Below will be the output

* Connected to localhost (::1) port 8080 (#0)
> POST /example HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
> 
< HTTP/1.1 201 Created
< Date: Sat, 10 Jul 2021 10:40:33 GMT
< Content-Length: 28
< Content-Type: text/plain; charset=utf-8
< 
* Connection #0 to host localhost left intact
{"message":"Status Created"}

As you can see from the output, it will correctly return the 201 status code along with the body.

You can also directly pass 201 to the WriteHeader function to send the 201 response.

w.WriteHeader(201)

Try it out, it will work.

We mentioned that we don't call WriteHeader explicitly then the call to Write function will call the WriteHeader function internally with status code 200 which is StatusOk. Let's see an example of that-

package main

import (
	"encoding/json"
	"log"
	"net/http"
)

func main() {
	handler := http.HandlerFunc(handleRequest)
	http.Handle("/example", handler)
	http.ListenAndServe(":8080", nil)
}

func handleRequest(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	resp := make(map[string]string)
	resp["message"] = "Success"
	jsonResp, err := json.Marshal(resp)
	if err != nil {
		log.Fatalf("Error happened in JSON marshal. Err: %s", err)
	}
	w.Write(jsonResp)
	return
}

See the code above. We haven't called the WriteHeader function anywhere. The program therefore should send the status code 200 by default.

Run the above program. It will start a server on 8080 port on your local machine. Now make the below curl call to the server

curl -v -X POST http://localhost:8080/example

Below will be the output

* Connected to localhost (::1) port 8080 (#0)
> POST /example HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
> 
< HTTP/1.1 200 OK
< Content-Type: application/json
< Date: Sat, 10 Jul 2021 16:24:11 GMT
< Content-Length: 21
< 
* Connection #0 to host localhost left intact
{"message":"Success"}

As you can notice from the output that it returns the 200 status code.

Also, check out our Golang advance tutorial Series - Golang Advance Tutorial

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